1. Field of the Invention
The present invention relates to a calculation method of the electro-magnetic field intensity of an electro-magnetic wave emitted from electronic equipment or the like, and more particularly, relates to an electro-magnetic field intensity calculation device using a different electro-magnetic field intensity calculation method, depending on whether an component constituting an electric circuit contained in an analysis target is liner or non-linear.
2. Description of the Related Art
With the high performance and miniaturization of equipment, an electro-magnetic wave emitted from electronic equipment has been called in question. With the complication of a circuit, the countermeasures of mis-operation of equipment due to noise voltage or the like also need great labor.
As a method for simulating an electro-magnetic wave emitted from electronic equipment, there are a variety of electro-magnetic analysis methods, such as a moment method and the like. In the moment method, the print-wired board, metal plate or the like of electronic equipment is divided into planar components called “patches”. Alternatively, for example, an antenna is divided into linear components called “wires”. Then, they are analyzed.
When applying an emitted electro-magnetic wave analysis to electronic equipment containing a non-linear component or the like, not only an electro-magnetic wave analysis but also a circuit analysis must be combined.
As analysis methods in which an electro-magnetic wave analysis and a circuit analysis are combined, the following reference is published.
Non-patent reference 1
J. A. Landt, “Network Loading of Thin-wire Antennas and Scatters in the Time Domain”, Radio Science, Vol. 16, pp 1241–1247 (1981).
This reference discloses the combination of an electro-magnetic wave analysis method called a “time domain moment method” and a circuit analysis method. In this analysis, a wire as an antenna is divided into a plurality of segments against an analysis target to which the antenna is connected, and an equation with n unknowns about unknown antenna current flowing through each segment and an equation with m unknowns about the current of a circuit network, thereby analyzing the electro-magnetic wave emitted from the analysis target.
When combining an electro-magnetic wave analysis and a circuit analysis thus, generally an analysis target is divided into a circuit analysis model containing a non-linear circuit component, an electro-magnetic wave analysis model composed of a wire, a patch and the like and a port for jointing the two models and is analyzed. However, in Non-patent reference 1, the analysis target is limited to the case of only one port and is analyzed, and a system represented by simultaneous equations with (n+m) unknowns is simplified into two systems of equations with n unknowns and equations with m unknowns, thereby capable of independently solving them. Then, antenna current is calculated and the electro-magnetic wave analysis is applied to the analysis target.
As another combination of a circuit analysis method and an electro-magnetic wave analysis method, there is the combination of a finite difference time domain (FDTD) electro-magnetic field analysis method and a circuit analysis method, which is disclosed by the following references.
Patent reference 1
Japanese Patent Application Publication No. H11-153634 “Simulation Device and Computer-readable Storage Medium Recording Simulation Program”
Patent reference 2
Japanese Patent Application Publication No. 2000-330973 “Hybrid Analysis Method for Combining Finite Difference Time Domain (FDTD) Electro-magnetic Field Intensity Method with Transient Electric Circuit Analysis Method and Hybrid FDTD Electro-magnetic Field/Transient Electric Circuit Analysis Device”
In the time domain moment method, a model itself is divided like an antenna is divided into segments, current flowing through the model is calculated and an electric or magnetic field intensity is calculated based on the calculated current. However, the FDTD method is characterized in that a space containing a model is divided into blocks and an electro-magnetic field intensity in the space can be directly calculated without calculating current.
Patent reference 1 discloses in a simulation apparatus cooperating an electromagnetic analysis and a circuit analysis, a simulation device capable of calculating a stable analysis result since the difference between a time when a transferred electric field intensity value is calculated and the time of an electric field intensity calculated by an electro-magnetic wave analysis reflecting the electric field intensity value decreases by transferring the electric field intensity value based on a circuit analysis (electric field intensity value of an area containing a circuit) to the electro-magnetic wave analysis when the time of the circuit analysis approaches a time when an electric field intensity should be calculated by the electro-magnetic wave analysis in a simulation device.
Patent reference 2 discloses a hybrid analysis method in which a FDTD method and a transient electric circuit analysis (TECA) method are combined.
By using simulation as an electro-magnetic wave countermeasure or a noise countermeasure, the cost-down of a prototype machine and measurement can be realized. As an actual simulator, a circuit simulator (such as SPICE, etc.) and an electro-magnetic field simulator (such as a simulator by the moment method, the FDTD method) are used for the noise and electro-magnetic countermeasures, respectively.
As described above, several combinations of an electro-magnetic wave analysis and a circuit analysis are proposed as a method for simulating an electro-magnetic wave emitted from electronic equipment containing a non-linear circuit component, such as a diode and the like. However, in Non-patent reference 1, the method can only be applied to a case where there is only one port as the jointing point of a model to which a circuit analysis should be applied and a model to which an electro-magnetic wave analysis should be applied, and cannot generally handle an analysis target in which a plurality of ports exist between the two model, which is a problem. Furthermore, in this reference, the voltage of the port of a transmission line without any failure is calculated, and cannot be calculated in a case where there is a hole in the ground layer or the like, which is another problem.
In the combination of the FDTD method and circuit analysis method like patent references 1 and 2, in order to, for example, calculate an electro-magnetic field intensity at a point 100 m away from a model, a space also including the point must be divided since the space including the model is divided into blocks, and the amount of calculation increases, which is another problem.
Since a space is divided into blocks, it is difficult to divide an antenna itself if an analysis target contains a linear component, such as a dipole antenna, a spiral antenna and the like, and sufficient calculation accuracy cannot be obtained, which is another problem.
Furthermore, when combining a circuit analysis method and an electro-magnetic wave analysis method, as described above, a port as the jointing point of the circuit analysis model and electro-magnetic wave analysis model is one corresponding to a circuit component constituting the electric circuit of an analysis target, generally corresponding to each of a plurality of components. Therefore, if the number of components is large, the linking process of the circuit analysis and electro-magnetic analysis takes time, which is another problem.
Generally, the respective calculation time intervals of a circuit simulator, such as SPICE, and an electro-magnetic wave simulator using the moment method or the like usually differ, and the matching of the times is needed. Therefore, the entire calculation time increases compared with a case where each of the simulators independently operates, which is another problem.
FIG. 1 shows this problem. In FIG. 1, times to be analyzed are plotted on the horizontal axis of each of the circuit analysis method and time domain moment method. However, at time t2 when the calculation of the moment method is made, no circuit analysis is made. Therefore, the calculation must be conducted after the time is returned, as shown below the horizontal axis of the circuit analysis side.